US3161656A - Unsaturated beta-lactones and method of preparing them - Google Patents

Description

United States Patent Ofifice 3,161,656 Patented Dec. 15, 1964 UNSATURATED ,B-LACTONES AND METHOD OF PREPARING THEM Edward U. Elam, Kingsport, Tenm, assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed hiay 9, 1961, Ser. N 108,749

Claims. (Cl. 260343.9)

This invention relates to novel unsaturated fl-lactones and to a novel method of preparation. More particularly, it relates 2,2,4,4-tetraalkyl-3-hydroxy-3-butenoic acid B-lactones and to their preparation by pyrolysis of diallryl ketene polymers.

groups which, with the carbon atom to which they are attached, form a 5 or 6 membered saturated carbocyclic ring. In accordance with my invention, these compounds are prepared by polymerizing a dialkyl ketene inthe presence of a strongly basic catalyst. The resulting solid linear polymer is then decomposed by pyrolysis to ob tain the novel lactones.

The lactones of my invention are valuable intermediates in the preparation of a number of useful chemicals. For example, when contacted with a strongly basic catalyst such as sodium methoxide in boiling ether or benzene, they'torm useful crystalline polymers. These polymers, though having the same infrared spectrum as the dialkyl ketene polymers from which the lactones are produced; have significant advantages over such polymers. For instance, the polymer made from the lactone does not evolve objectionable amounts of the monomeric keteue when The novel lactones are also useful as intermediates in the preparation of valuable allenic compounds. For instance, tetramethyl allene is produced ingood yield by pyrolysis of 2,zA-trimethyl-ll-hydroxy-il-pentenoic acid 3- lactone at a temperature, e.g., of 450 C.

As chemical reagents or intermediates -'the lactones of my invention have important advantages over the previ ously known dialkyl ketene dimers, i.e. the'tetraalkyl-L3- cyclobutanediones. For example, while tetramethyl-1,3- cylcobutancdione is a volatile, easily sublimed solid, the

isomeric lactoneisa liquidvai normal temperature and pressure and is, therefore, much more convenient to employ as a reagent. The two types of compounds can also be distinguished in their chemical reactions. In some reactions they give identical products but in others the products are quite difierent. Furthermore, the unsaturated B-lactones of the inventionl react with some compounds toward which the isomeric teuraalkylcyclobutanediones are completely inert.

The lactones of my invention are d ers of dialkyl ketenes but their properties are surprisingly different from those of such fi-lactone dimers as'diketene and the dimers of monoalkyl ketenes. My compounds are sufiiciently reactive for synthetic work but are much more stable than diketene and are less dangerous to handle and less sus ceptible to deterioration in storage. Diketene readily polymerizes on standing at room temperature while my compounds can be stored at normal temperature for long periods without polymerizing. \Vhen dilcetene is reacted in an inert solvent which contains a small amount of temperature can be used. Thepolymerization is highly catalyst (such as sodium ethylate) at 70-120 C., dehydroacetic acid is obtained in yields of 6080% [A. B. Boese, Jr., Ind. Eng. Chem. 32, 21 (1940)]. The 2,2,4,4- tetraalkyl-3-hydroxy-3butcnoic acid p-lactones, on the other hand, give only polymer under similar conditions. No compounds analogous to dehydroacetic acid are formed.

As I have indicated, the method of the present invention is essentially a two-stage method. In the first stage the dialkyl ketene starting material is polymerized under the influence of a strongly basic catalyst to form a" solid linear polymer. In the second stage this polymer is decomposed by pyrolysis to produce the fi-lactone dimer of the dialkyl ketene.

The starting materials for producing lactones of the formula,

by the method of my invention are disubstituted ketenes of the structure,

wherein the substituents, R, are alkyl groups of 1 to 4 carbon atoms or are alkylene'groups which, with the carbon atom to which they are attached, form a 5 or 6 membered saturated carbocyclic ring. Examples include dimethylketene, ethylmethylketene, diethylketene, butylethylketene, di-n-prdpylketene,diisobutylketene, di-n-butyllre l tene and carbocyclic ketenes such as tetramethyleneketene and pentamethylenelretene. I use the term dialkylketene to designate all of such disubstituted ketenes. The starting material can be one of such disubstituted ketenes or a mixture of two or more; In the latter event the lactone product can have any possible combination-of four sub stitnents of the typesnientioned w The polymerization stage of the process can be carried out over a wide range of conditions. For convenience and safety, it is preferable to prepare the polymer at or near room temperature, although much lower or higher exothermic so it is convenient to use asolvent or liquid reaction medium having a boiling point near the temperature at which the polymerization is to be carried out and to control the reaction temperature by refluxing the liquid. Ethyl ether is a particularly convenient reaction medium but other liquids such as dioxane, benzene, diisopropyl ether, hexane and the like can be used.

The degree to which the dialkyl ketene monomer is V polymerized in the polymerization stage can vary considerably. The intermediateqpolymer must be. of willcient chain length to be readily decomposable upon pyrolysis. However, extremely long chain length-or high molecular weight is unnecessary. In general, satisfactory re sults are obtained by polymerizing the monomer sufliciently to obtain a linear polymer having an average chain length of about 10 to 200 units.

The polymerization of the dialkyl ketcne monomer is carried out in the presence of a catalyst. Suitable catalysts are strongly basic materials. Best results are obtained with alcoholates or alkoxides of titanium or of elements of Groups I, II or 1H of the periodic table, such as sodium, potassium, lithium, calcium, aluminum or titanium ethoxi ie, propoxidc, butoxide, etc. These are the preferred polymerization catalysts. Other suitable catalysts include: other strongly basic substances whose 0.1 N aqueous solutions have a pH of at least 12, such as alkali metal hydroxides; calcium hydroxide; metal alkyls of titanium or of elements of Groups I, II or III of the periodic table, such as triethyl aluminum, amyl sodium or diethyl zinc; quaternary ammonium hydroxides such as trimethylbenzylamrnonium hydroxide and the like.

For catalyzing the polymerization reaction only a minor catalytic amount of the basic substance is required, and this is considerably less than one mol of catalyst per mol of dialkyl ketene. The amount of catalyst can vary somewhat depending on the polymerization temperature and other factors. Less catalyst is required for higher temperatures and more for lower temperatures. In gen eral, about 0.1 to 10 weight percent of catalyst based on the polymeric product gives satisfactory results.

The polymer obtained in the polymerization stage is subsequently decomposed by pyrolysis. The polymer is heated to a temperature sufiiciently high to yield the fl-lactone dimer as a vapor product but not so high as to decompose the lactone. The temperature at which the polymer decomposes to the p-lactone dimer depends, at least in part, upon its molecular weight. The lower molecular weight, ether-soluble polymers decompose to some extent in the range of 150-200 C. The higher molecular weight, etherinsoluble polymers melt at around 200 C. and decompose at about 280 C. To avoid decomposing the desired fl-lactone product, pyrolysis temperature should not exceed about 300 C.

The examples hereinafter illustrate preparation of my novel lactones and provide comparisons with other compounds.

Example 1 Dimethyl ketene, prepared by the pyrolysis of isobutyric anhydride, was passed into arstirred suspension of g. of sodium methylate in .1500 ml. of ethyl ether. The solution began to reflux vigorously within a few minutes, and a white, powdery solid began to separate. The mixture was allowed to stand overnight at room temperature; the yellow color of dimethyl ketene disappeared, and a large amount of white solid separated from the mixture. The polymer (252 g.) was recovered by filtration, washed thoroughly with water, and air'dried. It melted sharply at 175 C. Analysis-Calm. for (QH OL C, 68.6; H, 8.56. Found: C, 68.9; H, 8.81; mol. wt, 2640. 100 g. of this polymer was decomposed by distillation through a short distilling column at 100 mm. pressure. The polymer melted to a viscous liquid which decomposed smoothly, starting at about 20 C. Distillate was collected up to a head temperature of 150 C. (100 mm.) The distillate, which weighed 81 g., was redistilled through the same column to give 63.0 g. pf 2,2,44rimethy1-3-pentenoic acid fl-lactone boiling from 105-10 C. at 100 mm. This material was 87.2% pure by gas chromatography. The

structure wais proved by the infrared andnuclear magnetic resonance spectra, as well as by its reaction with amines to give amides of 2,2,4-trimethyl-3-oxovaleric acid. Arialya's.'-Calcd. for C l-1 0 C, 68.6; H, 8.56; mol. wt, 140. Found: C,"68.4; ,H, 8.53; mol. wt, 127-.

More 2,2,4-trimethyl-3-pentenoic acid fl-lactone was re-' hydrogenation of the unsaturated B-lactones of the invention. a

Example 2 140 g. 1 mole) of 2,2,4-trimethyl-3-hydroxy-3-pentenoic acid B-lactone was hydrogenated for six hours over g. of 5% palladuim on almurnina at 100 C., 3000 p.s.i. Gas chromatographic analysis of the product indicated that it consisted essentially of 3-hydroxy-2,2,4-trimethyl- Z5 Example 3 A mixture of 93.1 g. (1 mole) of aniline and 1.40 g. (1 mole) of 2,2,4-trimethyl-3-hydroxy-3 pentenoic acid fi-lactone was heated on a steam bath for three hours,-

then allowed to stand at room temperature overnigh The product solidified completely; after one recrystallization from d-iisopropyl ether, pure 2,2,4-trimethyl-3- oxovaleranilide, M.P. 93.5-94.5" C., was obtained in 93% yield. The melting point of the product was not changed by further recrystallization.

The following example illustrates the failure of tetramethyl-1,3-cyclobutanedione to react with aniline under conditions similar to those of Example 3.

Example 4 A solution of 140 g. (1 mole) of tetramethyl-l,3-eyclobutanedione and 232.5 g. (2.5 moles) of aniline in 300 ml. of xylene was refluxed for two days. Unchanged tetramethyl-l,3-cyclobutanedione was recovered in essentially quantitative yield on distillation of the reaction mixture.

Example 5 below illustrates the polymerization of 2,2,4- uimethyl-3-hydroxy-3-pentenoic acid fl-lactone in the presence of base.

Example 5 5 g. of sodium methoxide was added to "a solution of ml. of 2,2,4-trhnethyl-3-hydroxy-3-pentenoic acid 43- -lactone in 100 ml. of toluene. Anexotherrnicv reaction took place; after it had subsided, the-nfixture was'refluxedfor 2% hours, then allowed to cool. The mixture became semisolid; on filtering, 80.4 g'. of a low-molecular-weight polymer which melted at about 170 C. was obtained. The intrinsic viscosity of this polymer, measured in phenol- .tetrachloroethane, was 0.09.

Example 6 below demonstrates the preparation of an unsaturated fl-lactone of the invention from a dialkyl -ketene of which the alkyl groups are not identical.

Example 6 50 g. of ethylmethylketene was polymerized as described in Example 1. The resulting polymer was ethersolube. Evaporation of the ether solution, after filtering 0d the sodium methoxide, gave a syrupy polymer which was pyrolyzed by distillation at 100 mm. to give a crude fraction boiling from -195" C. (100 mm.) which was shown by gas chromatography'and infrared analysis to consist mainly of 2,4-dimethyl-2'ethyl-3-hydroxy-3-hexe-' noic acid fldaotone.

Example 7 below demonstrates the "preparation of an unsaturated fl-lactone of the invention from diethylketene.

Example 7 A solution of 10 ml. of diethylketene in 20 ml. of dry toluene was kept under a nitrogen atmosphere, cooled to 75 C., and treated with 0.108 g. of butyl lithium. A polymer was obtained which, on pyrolysis, gave 3-hy droxy-2,2,4-triethyl-3-hexenoic acid fl-lactone, El. 30 C. (25 mm.).

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described herein above and as defined in the appended claims.

I claim:

1. An unsaturated fi-lactene of the formula wherein the substituents, R, taken singly, are unsubstituted alkyl groups of 1 to 4 carbon atoms and, taken collectively, are unsubstituted alkylene groups which, with the carbon atom to which they are attached, form a saturated carbocyclic ring of 5 to 6 carbon atoms.

2. A 2,2,4,4-tetraalkyl-3-hydroxy-3-butenoic acid B-lactone wherein the alkyl groups are unsubstituted and have from 1 to 4 carbon atoms.

3. 2,2,4,4-tetramethyl-3-hydroxy-3-butenoic acid fl-lactone.

4. 2,4 dimethyl-2-ethyl-3-hydroxy-3-hexenoic acid B- lactone.

5. 3-hydroxy-2,2,4-triethyl-3-hexenoic acid fl-lactone.

6. The method of preparing 2,2,4,4-tetraalkyl-3-hydroxy-3-butenoic acid fi-lactones which comprises contacting a dialkyl ketene of which the alkyl substituents have from 1 to 4 carbon atoms with a strongly basic polymerization catalyst under polymerization conditions, recovering a solid polymer, decomposing said polymer by pyrolysis and recovering a product comprising such lactone.

7. The method of preparing 2,2,4,4-tetraalkyl-3-hydroxy-S-butenoic acid fi-lactones which comprises contacting a dialkyl ketene of which the alkyl substituents have from 1 to 4 carbon atoms with an alkali metal alkoxide catalyst under polymerization conditions and in the presence of a volatile liquid reaction medium, separating a solid polymer from the liquid reaction medium, heating the polymer to pyrolysis temperature and recovering a distillate product comprising said 2,2,4,4-tet1'aalkyl-3-hydroxy-3-butenoic acid fi-lactone.

8. The method of preparing 2,2,4 trimethyl-3-hydroxy-3-pentenoic acid fl-lactone which comprises forming a reaction mixture of dimethyl ketene with a suspension of a catalytic amount of sodium methylate in ethyl ether at room temperature, maintaining the reaction mixture at the boiling temperature of the ether at atmospheric pressure, recovering a solid polymer from the reaction mixture, heating the polymer to pyrolysis temperature and recovering the evolved vapor comprising 2,2,4-trimethyl- 3-hydroXy-3-pentenoic acid ,B-lactone.

9. The method of preparing 2,4-dimethyl-2-ethyl-3-hydroxy-B-hexenoic acid B-lactone which comprises forming a reaction mixture of ethylmethylltetene with a suspension of a catalyti amount of sodium methylate in ethyl ether at room temperature, maintaining the reaction mixture at the boiling temperature of the ether at atmospheric pressure, separating a viscous polymer from the reaction mixture, heating the polymer to pyrolysis temperature and recovering a product comprising 2,4-dimethyl-2-ethyl-3- hydroxy-3-hexenoic acid fi-lactone.

10. The method of preparing 3-hydroXy-2,2,4-triethyl- 3-hexenoic acid ,B-lactone which comprises forming a reaction mixture of diethyl ketene, toluene and butyl lithium in an inert atmosphere at a temperature of about C., recovering a viscous polymer, decomposing said polymer by pyrolysis and recovering a product comprising 3- hydroxy-2,2,4-triethyl-3-hexenoic acid fi-lactone.

References Qited in the file of this patent UNITED STATES PATENTS Theobald Apr. 13, 1954 Hartle Oct. 10, 1961 OTHER REFERENCES

Claims (1)

1. AN UNSATURATED B-LACTONE OF THE FORMULA